Microwave power amplifiers operate with ever increasing constraints on the amount of power that they may emit at frequencies outside the band of interest. For example, it may be desirable to limit the amount of power that a microwave power amplifier is able to emit in a certain frequency band outside the frequency of operation. Power emitted within the band of interest may be referred to as “in-band power,” while power outside the frequency of operation may be referred to as “out-of-band power.” In some applications, control of out-of-band power may be desired to prevent interference between adjacent communication channels. In other applications, control of out-of-band power may be useful in situations where, through either damage to an amplifier or excursions in manufacturing, a microwave transistor amplifier becomes unstable and oscillates, producing high levels of out-of-band power.